Process for the formation of novel acrylamide acrylate copolymers

ABSTRACT

The present invention relates to a process for the formation of water soluble copolymers of acrylamide and alkyl poly(etheroxy)acrylate which are excellent viscosification agents, wherein the process includes the free radical copolymerization of acrylamide monomer and alkyl poly(etheroxy)acrylate monomer in an aqueous medium under nitrogen conditions in the presence of free radical initiator at a sufficient temperature and for a sufficient time to effect copolymerization.

BACKGROUND OF THE INVENTION

Polyacrylamide (PAM) and hydrolyzed polyacrylamide (HPAM) are commonwater soluble polymers that have found application in oil fieldchemicals, paints, paper making, cosmetics, etc. The solution rheologyof these materials define their use in these applications. With thesepolymers, aqueous viscosification or thickening is achieved through acombination of high molecular weight and chain expansion due torepulsion of pendent ionic groups along the polymer chain. Highmolecular weight polymers are difficult to prepare and dissolve and arealso sensitive to shear. Viscosification due to charge repulsion is saltsensitive and thus, finds limited utility in highly saline systems.

Polymerizable esters of acrylic acid or methacrylic acid with alkyl oralkylaryl poly(ethyleneoxy) ethyl alcohols are disclosed in DicksteinU.S. Pat No. 4,075,411. ##STR1## Trecker, U.S. Pat. No. 3,896,161 andBritish Pat. No. 828,496. Such monomers have found use in thepreparation of stable latexes and special textiles.

Copolymers of base-neutralized acrylic acid and nonionic surfactantacrylates have also found use as thickeners for both aqueous solutionsand water/organic liquid emulsions (Koenig and Bryant, U.S. Pat. No.4,268,641). Improved NaCl tolerance is also taught therein. A liquidcomposition useful as a thickening agent in polymer latexes, comprisinga mixture of solvent and a terpolymer of acrylic acid, an ester of theformula of: ##STR2## and an alkyl acrylate or methacrylate is claimed inU.S. Pat. No. 4,138,381.

PRESENT INVENTION

Unlike the prior art, the present invention discloses substantiallycopolymers of acrylamide and nonionic surfactant monomers such as##STR3## where R₁ =alkyl, C₁ -C₂₀ ; aryl, C₆ -C₃₀ ; alkylaryl, C₆ -30;and R₂ =H or CH₃ ; n=1-60. These surfactant monomers can be referred toas alkyl poly(etheroxy)acrylates or R--PEO--AC.

The compositions of the instant invention are distinguished fromnonionic polyacrylamide homopolymers by their higher solutionrheological behavior, e.g., viscosification efficiencies. They aredifferent from hydrolyzed polyacrylamide, a copolymer of acrylic acidand acrylamide, by virtue of their higher thickening ability andconcentration dependence of viscosity in a brine environment and oftenhigher retention of viscosity in the presence of inorganic electrolytes.Of course, viscosities of polymer solutions containing inorganicelectrolytes are a function of such factors as polymer structure,molecular weight, concentration, amount of alkyl (etheroxy)acrylate,etc.

The present invention is distinct from the acrylic acid salt andnonionic surfactant acrylates of Koenig and Bryant because differentcomonomers (i.e., acrylamide vs. salts of acrylic acid) and aqueous,rather than hydrocarbon emulsion polymerization methods, are used.Moreover, the instant copolymers are prepared in a one-step process,i.e., neutralization is not required. Acrylic acid-based polymers are tobe avoided because of the known susceptibility of acrylic acid (and itssalts) to precipitation by polyvalent cations (e.g., Ca⁺⁺); the latterspecies are often found in geological formations. (F. J. Glaris in"Water Soluble Resins 2nd Ed", R. L. Davidson and M. Sittig, Eds.,Rheinhold, N.Y., p. 168).

The instant invention describes a novel class of acrylamide copolymerscontaining alkyl poly(etheroxy) acrylate groups. These copolymers arewater soluble and many exhibit salt insensitive aqueous viscosification.The mechanism of solution viscosity enhancement is different from thatfound in the prior art systems based on polyacrylamide and hydrolyzedpolyacrylamide. In the compositions of the present invention, thepresence of a small amount of hydrophobic or water insoluble alkyl groupon the surfactant comonomer is believed to result in intermolecularaggregation or interaction in solution. This aggregation results inenhanced viscosity relative to a noninteracting polymer such aspolyacrylamide. Furthermore, the presence of ethylene oxide groups onthe surfactant comonomer can be used to adjust polymer solubility andinfluence viscosity. The relative salt insensitivity of the solutionviscosity of these novel copolymers distinguishes them from viscosifiersbased on charge repulsion such as hydrolyzed polyacrylamide.

SUMMARY OF THE INVENTION

The present invention relates to unique and novel water solublecopolymers of acrylamide and alkyl poly(etheroxy)acrylate. Thesepolymers are prepared by a free radical copolymerization process,wherein the acrylamide monomer and alkyl poly(etheroxy)acrylate monomerare added to deoxygenated water under a nitrogen purge; thepolymerization solution is heated to a temperature sufficient toactivate the initiator; free radical initiator is added to thepolymerization solution to initiate polymerization; polymerizing theacrylamide monomer and alkyl poly(etheroxy)acrylate monomer for asufficient time and at a sufficient temperature to form the watersoluble copolymer of acrylamide and alkyl poly(etheroxy)acrylate; andrecovering the formed water soluble copolymer from the polymerizationsolution. Many of these water soluble copolymers of acrylamide and alkylpoly(etheroxy)acrylate are excellent viscosification agents in saltwater.

GENERAL DESCRIPTION

The water soluble copolymers of acrylamide and alkylpoly(etheroxy)acrylate of the present invention are formed by a freeradical copolymerization process in an aqueous medium. These watersoluble copolymers of acrylamide and alkyl poly(etheroxy)acrylate areuseful as viscosifiers in water and in aqueous solutions containinginorganic electrolytes.

The free radical copolymerization process used to form these watersoluble copolymers of acrylamide and alkyl poly(etheroxy)acrylatecomprises adding acrylamide monomer to deoxygenated water under anitrogen atmosphere; adding alkyl poly(etheroxy)acrylate monomer to thesolution of water and acrylamide monomer to form the polymerizationsolution; heating the polymerization solution to a sufficienttemperature to activate the initiator; adding free radical initiator tothe polymerization solution to cause initiation of the copolymerizationof the acrylamide monomer and the alkyl poly(etheroxy)acrylate monomer;copolymerizing the acrylamide monomer and alkyl poly(etheroxy)acrylatemonomer at a temperature of at least 5° C. for at least 2 hours, morepreferably at least 20° C., to form the water soluble copolymer ofacrylamide and alkyl poly(etheroxy)acrylate; and recovering byprecipitation or dialysis of the formed water soluble copolymer ofacrylamide and alkyl poly(etheroxy)acrylate from the polymerizationsolution.

The water soluble copolymers of acrylamide and alkylpoly(etheroxy)acrylate can be substantially represented by the formula:##STR4## wherein R₁ is selected from the group consisting of C₁ to C₂₀alkyl groups, C₆ to C₂₀ aryl groups and C₆ to C₃₀ alkylaryl groups; R₂is hydrogen or a methyl group, n is about 1 to about 60, more preferablyabout 5 to about 50, and most preferably about 8 to about 45; y is about0.01 to about 5.00 mol.%, more preferably about 0.04 to about 3.0, andmost preferably about 0.1 to about 1.5; and x is about 95.00 to about99.96 mole %, more preferably about 97.0 to about 99.06 and mostpreferably about 99.9 to about 98.5. Typical, but nonlimiting examplesof preferred R groups are methyl, octadecyl, phenyl and nonylphenyl.

The instrinsic viscosity of the water soluble copolymers of acrylamideand alkyl poly(etheroxy)acrylate is about 1 to about 25, more preferablyabout 2 to about 20, and most preferably about 3 to about 10. Theintrinsic viscosity, [η], is related to the viscosity average molecularweight, Mv, by the Mark Houwink relationship: [η]=KM_(v).

Suitable alkyl poly(etheroxy)acrylate monomers useful in the preparationof the water soluble copolymers of the instant invention are methyl,dodecyl, octadecyl phenyl, octylphenyl, and nonylphenyl.

Suitable free radical initiators for the instant free radicalcopolymerization process include potassium persulfate,2,2'-azobisisobutyronitrile (AIBN), H₂ O₂, and ethanolamine/sodiumsulfite. The concentration of the free radical initiator is about 0.01to about 1.0 grams per 100 grams of the acrylamide monomer and alkylpoly(etheroxy)acrylate monomer.

The concentration of the acrylamide monomer and alkylpoly(etheroxy)monomers in the aqueous polymerization solution is about 1to about 20 grams of acrylamide monomer and alkyl poly(etheroxy)monomerper 100 grams of water, more preferably about 3 to about 15, and mostpreferably about 3 to about 10. Copolymerization of the acrylamidemonomer and alkyl poly(etheroxy)acrylate monomer is effected at atemperature of about 5° to about 80° C., more preferably about 20 toabout 60, and most preferably about 40 to about 60 for a period of timeof about 0.5 to about 48 hours, more preferably about 2 to about 30, andmost preferably about 4 to about 24.

Copolymers of acrylamide and alkyl poly(etheroxy)acrylate are recoveredfrom the polymerization solution by precipitation with a nonsolvent(e.g., methanol, isopropanol, or acetone), followed by vacuum drying. Analternative recovery technique involves dialysis followed by freezedrying. Alternatively, dialysis can be used. The water solublecopolymers can be either dried by vacuum or by freeze drying means.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a plot of reduced viscosity versus concentration foran acrylamide polymer, a hydrolyzed acrylamide polymer and a copolymerof acrylamide and alkyl poly(etheroxy)acrylate.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following examples illustrate the present invention without,however, limiting the same hereto.

EXAMPLE 1 Polyacrylamide Polymerization

A 500-1000 ml quantity of distilled water was added to a resin flaskequipped with a water condenser, thermometer, mechanical stirrer, aswell as a nitrogen inlet and outlet. The water was deoxygenated for15-30 minutes by a nitrogen purge. The acrylamide monomer (AM)(0.42-0.49 mol), Aldrich, was added and the solution further purged at50° C. with nitrogen for 3/4 to 1 hour. The K₂ S₂ O₈ initiator(0.005-0.05 g) was charged and the polymerization temperature maintainedat 50°-55° C. The polymerization was run for about 18.5-24 hours(conversion 90-100%). Polymers were isolated/purified by precipitationin acetone and vacuum drying. An alternative procedure for isolation andpurification involved dialysis of a diluted polymer solution followed byfreeze drying. Table I describes homopolymerization according to themethod of this Example.

                  TABLE I                                                         ______________________________________                                        Homopolymers of Polyacrylamide (PAM)                                          Sample #  AM mol       H.sub.2 O ml                                                                           K.sub.2 S.sub.2 O.sub.8                       ______________________________________                                                                        gm                                            9020-74CG .42           500     .05                                           9020-3P   .42          1000     .01                                           9595-53P  .42          1000      .005                                         9020-117P .49           500     .01                                           ______________________________________                                    

EXAMPLE 2 Copolymerization of Acrylamide with AlkylPoly(etheroxy)acrylates (R--PEO--AC)

A 500-1000 ml quantity of distilled water was added to a resin flaskequipped with a water condenser, thermometer, mechanical stirrer, aswell as a nitrogen inlet and outlet. Nitrogen was bubbled through thesolution for 15-30 minutes. The acrylamide (AM), Aldrich, monomer(0.21-0.42 mol) and alkyl poly(etheroxy)acrylate (R--PEO--AC) monomers(0.42-8.5×10⁻³ mol) were charged to the flask. The alkyl poly(etheroxy)acrylate monomers used were commercial products of the Monomer-Polymerand Dajac Laboratories, e.g. 8615, 8616, 8617, and were used asreceived. The solution was heated by an oil bath under nitrogen purge at50° C. for 1 hour. After this period of time, the K₂ S₂ O₈ initiator(0.005-0.1 g) was added and the temperature maintained at 50°-55° C.under nitrogen for about 18.5-24 hours (Conversion 70-95%). Polymerswere purified by precipitation or dialysis techniques. Polymers weredried by vacuum or freeze drying. Table II describes copolymerizationprepared according to this Example. The surfactant acrylate content isindicated as mole % of monomer charge.

                                      TABLE II                                    __________________________________________________________________________    Copolymerization of Acrylamide and Alkyl Poly(etheroxy) Acrylates                                  Comonomer                                                        AM Comonomer Type                                                                          Mol    Mole % H.sub.2 O                                                                        K.sub.2 S.sub.2 O.sub.8                 Sample #                                                                              mol                                                                              R-   (PEO).sub.x                                                                        × 10.sup.3                                                                     Comonomer                                                                            ml g                                       __________________________________________________________________________    9595-9P .42                                                                              C.sub.9 H.sub.19 Ph                                                                40   .42    0.1    500                                                                              .01                                     9020-26DY                                                                             .42                                                                              C.sub.9 H.sub.19 Ph                                                                40   1.2    0.3    500                                                                              .01                                     9020-121-DFD                                                                          .42                                                                              C.sub.9 H.sub.19 Ph                                                                40   1.2    0.3    500                                                                              0.1                                     9595-54P                                                                              .42                                                                              C.sub.9 H.sub.19 Ph                                                                40   1.2    0.3    1000                                                                             .005                                    9020-33DM                                                                             .21                                                                              C.sub.9 H.sub.19 Ph                                                                40   1.2    0.6    500                                                                              .1                                      9595-10P                                                                              .42                                                                              C.sub.9 H.sub.19 Ph                                                                40   8.5    2.0    500                                                                              .01                                     9020-136                                                                              .21                                                                              C.sub.9 H.sub.19 Ph                                                                10   1.6    0.8    500                                                                              .005                                    9020-138P                                                                             .21                                                                              C.sub.9 H.sub.19 Ph                                                                10   3.2    1.5    500                                                                              .005                                    9020-61 .21                                                                              C.sub.9 H.sub.19 Ph                                                                10   3.2    1.5    500                                                                              .05                                     9020-139P                                                                             .21                                                                              C.sub.9 H.sub.19 Ph                                                                10   6.9    3.2    500                                                                              .005                                    9595-3P .42                                                                              CH.sub.3                                                                           40   1.2    0.3    500                                                                              .01                                     9020-154P                                                                             .21                                                                              Ph   30   1.2    0.3    500                                                                              .01                                     9595-103                                                                              .42                                                                              C.sub.18 H.sub.35                                                                  35   1.3    0.3    500                                                                              .01                                     9595-153P                                                                             .42                                                                              Ph   1    1.3    0.3    500                                                                              .01                                     __________________________________________________________________________

EXAMPLE 3 Polymer Solution Properties

The polymers were weighed (±0.001 g) into flasks; the solvents (doubledistilled H₂ O, salt added where necessary) were weighed into the sameflask. The polymers were allowed to agitate on a magnetic stirrer for aminimum of 48 hours or until complete solubility was achieved, asdetermined by visual observation. In the event a polymer solutiondisplayed "gel" particles after a lengthy dissolution period, thesolution was centrifuged at 2000 rpm for two hours to separate the "gel"from the soluble portion. A few of the more viscous solutions weresubjected to an additional filtration through a 150 mesh stainless steelscreen to remove any microgel particles. An aliquot was then removed andvacuum dried at 110° C. to determine solubility and polymerconcentration for all polymers. When polymer solubility did notapproximate 90%, polymer concentrations were corrected.

A portion of the stock polymer solution was removed and to a knownweight of solution was added 2 wt.% NaCl. Dilutions of each polymerstock solution were prepared and viscosity obtained after waiting aminimum of one hour after dilution to achieve equilibrium. The reducedviscosity or viscosity number ##EQU1## where η_(s) is the polymerslution viscosity (centipoise), η_(o) is the solvent viscosity and c isthe polymer concentration was used to compare various polymer solutionsat different concentrations. Polymer concentration began at 3000 ppm toestablish an initial baseline prior to dilution. Viscosity measurementswere conducted at 25° C. on a Contraves Viscometer at 1.285 sec⁻¹.Typical data are shown in Table III. Intrinsic viscosity, [η], definedas the limit of reduced viscosity as polymer concentration goes to zero,is given in this table as dl/g. Viscosity η at shear rate at 1.2 g⁻¹ hasthe units of cps.

                                      TABLE III                                   __________________________________________________________________________    Polymer Solution Properties                                                                             Charged                                                                              Conc. of  NaCl     %                                Homo- or                                                                            Comonomer Type                                                                             Mole % Polymer                                                                            [η]                                                                            Conc.                                                                              η at                                                                          Re-                       Sample #                                                                             Copolymer                                                                           R     --(PEO)--                                                                            Comonomer                                                                            ppm  2% NaCl                                                                            % w/w                                                                              1.28s.sup.-1                                                                      tention                                                                           Comments              __________________________________________________________________________    9020-74CG                                                                            Homo- --    --     --     3000 1.6  0.0  3.0 --  Low MW                       (PAM)                               2.0  3.0 100                       Polysciences                                                                         Homo- --    --     --     3000      0.0  6.6 --                               (PAM)                               2.0  4.0 60                        9020-3P                                                                              Homo- --    --     --     3000      0.0  14.0                                                                              --                               (PAM)                               2.0  8.0 57                        9020-117P                                                                            Homo- --    --     --     3000 9.0  0.0  18.0                                                                              --  High MW                      (PAM)                               2.0  7.0 39                        9595-53P                                                                             Homo- --    --     --     3000 10   0.0  --  --  High MW                      (PAM)                               2.0  8.4 --                        Dow Pusher.sup.(1) 700                                                               Co (HPAM)                                                                            ##STR5##    35.sup.(1)                                                                           3000 24   0.0 2.0                                                                            1250 50                                                                           -- 4                                                                              High MW + Ionic       9595-9P                                                                              Co    C.sub.9 H.sub.19 Ph                                                                 40     0.1    3000 5.6  0.0  6.9 --  High MW;                                                         2.0  7.5 109 low                                                                           [comonomer]           9020-121DFD                                                                          Co    C.sub.9 H.sub.19 Ph                                                                 40     0.3    3000 3.0  0.0  136 --  High MW;                                                         2.0  98  72  higher                                                                        [comonomer]           9020-26DY                                                                            Co    C.sub.9 H.sub.19 Ph                                                                 40     0.3    3000 4.0  0.0  65  --                                                                   2.0  75  115                       9595-54P                                                                             Co    C.sub.9 H.sub.19 Ph                                                                 40     0.3    3000      0.0  --  --  High MW;                                                         2.0  233 --  higher                                                                        [comonomer]           9020-33DY                                                                            Co    C.sub.9 H.sub.19 Ph                                                                 40     0.6    3000 2.1  0.0  8.0 --  Low MW;                                                          2.0  6.0 75  higher                                                                        [comonomer]           9595-10P                                                                             Co    C.sub.9 H.sub.19 Ph                                                                 40     2.0    2000 6.2  0.0  36  --  High                                                             2.0  2.0 5.5 MW; High                                                                      [comonomer];                                                                  Low                                                                           [polymer]             9020-61                                                                              Co    C.sub.9 H.sub.19 Ph                                                                 10     1.5    3000 7.5  0.0  8.0 --  Moderate                                                         2.0  6.0 75  MW;                                                                           Moderate                                                                      [comonomer]           9020-138P                                                                            Co    C.sub.9 H.sub.19 Ph                                                                 10     1.5    3000      0.0  35  --  High MW;                                                         2.0  5   14  Moderate                                                                      [comonomer]           9020-139P                                                                            Co    C.sub.9 H.sub.19 Ph                                                                 10     3.2    1500 1.6  0.0  21  --  High                                                             2.0  1.6 7.6 [comonomer];                                                                  Low                                                                           [polymer];                                                                    Low MW                9595-3P                                                                              Co    CH.sub.3                                                                            40     0.3    3000      0.0  5.0 --                                                                   2.0  5.0 100                       9595-154P                                                                            Co    Ph    40     0.3    3000 6.0  0.0  4.0 --                                                                   2.0  4.0 100                       9595-103                                                                             Co    C.sub.18 H.sub.35                                                                   35     0.3    3000 8.0  0.0  7.2 --                                                                   2.0  5.6 77                        9595-153P                                                                            Co    Ph     1     0.3    3000 8.0  0.0  9.0 --                                                                   2.0  8.0 89                        __________________________________________________________________________     .sup.(1) Dow Pusher 700 is a commercial copolymer of acrylamide and sodiu     acrylate (35%).                                                          

EXAMPLE 4 Polymer Solution Properties: Instant Copolymers vs. PAM

Table III clearly shows that the instant copolymers, especially thecopolymers of nonylphenoxy poly(etheroxy)acrylates, are more efficientviscosifiers than homopolyacrylamide (PAM). Particular attention iscalled to polymers prepared at similar initiator and monomer chargesbecause the ratio of [m]/√[I] is related to polymer molecular weight,ceteris paribus. For example, the viscosity of copolymer 9595-54P can becompared with that of homopolymer 9595-53P. The viscosities of 3000 ppmsolutions at 1.28 sec⁻¹ shear rate are 233 cps and 8.4 cps respectively.This viscosity increase (approximately 30-fold) is associated with theaddition of only 0.3 mole % of the acrylate comonomer to acrylamide.

EXAMPLE 5 Polymer Solution Properties--Salt Tolerance

Table III also shows the excellent tolerance of some of the presentcopolymers to a brine (2% NaCl) environment. Attention is called tocolumn (% η retention) for the instant copolymers compared with PAM andHPAM (a copolymer of acrylamide and sodium acrylate). In the preferredrange of this invention (at low alkyl poly(etheroxy)acrylate R--PEO--ACcontent and/or low polymer concentrations), the instant copolymers aresubstantially more resistant to brine than HPAM (% η retention=72-115%vs. 4%). At high R--PEO--AC contents (e.g., Sample 9595-10P with 2 mol %comonomer), the solubility limit of the polymer is approached and suchcomparisons are inappropriate. Of course, the solubility and degree ofsalt tolerance varies for each copolymer depending upon many factors,e.g., the level of R--PEO--AC, the length of PEO chain, the nature of R,the molecular weight of the polymer, the concentration of the polymer,etc. It is understood that the instant disclosure is presented by way ofexample and should not be considered as limiting.

EXAMPLE 6 Polymer Solution Properties Brine ThickeningEfficiency--Instant Copolymers vs. PAM and HPAM

FIG. 1 illustrates the advantages of the compositions of the instantinvention compared with PAM and HPAM of the prior art. This figurepresents reduced viscosity-concentration plots for the R--PEO--ACcopolymers (0.3 mole %) compared with PAM and HPAM (Dow Pusher 700).Clearly, the instant copolymers are more efficient brine viscosifiersthan PAM. In fact, the present copolymers even surpass the viscosity ofthe commercial copolymer HPAM above certain concentrations. This resultis all the more noteworthy in view of the fact that the molecularweights of the disclosed copolymers are likely to be substantially lessthan that of HPAM, based upon intrinsic viscosity measurements. The[η]_(2%NaCl) of the instant copolymers (e.g., 9020-121DFD and 9020-26DY)are 3-4 while that of HPAM is 24 (Table III).

What is claimed is:
 1. A free radical copolymerization process for theformation of a water soluble copolymer of acrylamide/alkylpoly(etheroxy)acrylate which comprises the steps of:(a) forming anaqueous reaction solution from a water soluble acrylamide monomer,deoxygenated water under a nitrogen atmosphere and a water soluble alkylpoly(etheroxy)acrylate; (b) heating said reaction solution to at least50° C.; (c) adding sufficient free radical initiator to said reactionsolution to initiate copolymerization of said acrylamide monomer andsaid alkyl poly(etheroxy)acrylate monomer; and (d) polymerizing saidacrylamide monomer and said alkyl poly(etheroxy)acrylate monomer in saidreaction solution for a sufficient period of time, at a sufficienttemperature to form said copolymer.
 2. A free radical copolymerizationprocess according to claim 1, further including means for recoveringsaid copolymer from said reaction solution.
 3. A free radical processaccording to claim 1 wherein said copolymer is water soluble.
 4. A freeradical process according to claim 3 wherein said copolymer hassubstantially the formula: ##STR6## wherein R₁ is selected from thegroup consisting of C₁ to C₂₀ alkyl groups, C₆ to C₂₀ aryl groups and C₆to C₃₀ alkylaryl groups, R₂ is hydrogen or methyl group, n is about 23to 60, y is about 0.01 to about 5.00 mole %, and x is about 95.00 toabout 99.99 mole %.
 5. A free radical copolymerization process accordingto claim 1 wherein said R₁ is an alkyl group having about 1 to about 20carbon atoms.
 6. A free radical copolymerization process according toclaim 4 wherein n is about 1 to about 60 mole %, y is about 0.04 toabout 3.0 mole % and x is about 97.0 to about 99.0 mole %.
 7. A freeradical copolymerization process according to claim 1 wherein saidreaction solution is maintained at a temperature of at least about 40°C. for at least about 5 hours.
 8. A free radical copolymerizationprocess accordig to claim 1 wherein said free radical initiator isselected from the group consisting of AIBN, H₂ O₂, H₂ O₂ /Fe, H₂ O₂ /Ce(IV), and potassium persulfate.